Method and apparatus for adjusting the boundary surface between two controllably flowing and mutually separable and for conducting both solutions out of the separation part

ABSTRACT

The invention relates to a method for adjusting the boundary surface between the two mutually separable solutions in liquid—liquid extraction at the discharge end of the separation part and for preventing the aeration of the solutions when discharging them from the separation part, so that the overflow height of the settled, lighter organic solution is maintained constant. In order to adjust the boundary surface in between the mutually separable solutions, the overflow height of the heavier aqueous solution is adjusted by conducting the settled aqueous solution from down upwards through tubular elements, in which case the height of these overflow pipes can be adjusted. The aeration of the solutions when discharging them from the separation part is prevented by conducting the solutions into transfer pipes through covered, shaft-like weir boxes that are deeper than the discharge end. The invention also relates to an apparatus whereby the boundary surface between the solutions is adjusted and the aeration prevented.

FIELD OF THE INVENTION

The invention relates to a method for adjusting the boundary surface orthe location of the dispersion zone in the vertical direction inliquid—liquid extraction, in between two solutions that are mutuallyseparable owing to gravity, and to a method for conducting the separatedsolutions out of the space where the separation takes place,advantageously so that an aeration of the solutions in the transfer stepis prevented. The invention also relates to an apparatus for realizingthe method.

BACKGROUND OF THE INVENTION

In large extraction plants, such as copper extraction, the adjusting ofthe solution boundary surfaces and the discharging of the solutions arecombined by adopting two collecting chutes provided with solutionoverflows, which chutes extend vertically over the whole final end ofthe separation part. Generally there are used two attached chutes, thefirst of which—in the solution flow direction—is a fixed chutecollecting the lighter organic solution as overflow, and the latter is achute collecting the aqueous solution, provided with an adjustableoverflow edge. The heavier solution, i.e. the aqueous solution, isconducted from underneath both chutes through a duct formed in betweenthe chute bottoms and the separation part bottom. From this duct, theaqueous solution turns up and flows in the form of a U-turn in thecollecting chute, in a direction that is opposite to the originalflowing direction.

The adjustable overflow of the aqueous solution is formed of an outeredge of an aqueous solution chute, known in the prior art, which isconstructed of a wall plate extending up to a given height and ofanother plate moving against it. This structure, provided with ahorizontal overflow edge, serves as the basic overflow level, arrangedat a height which it is unnecessary to go below from the adjusting pointof view. The adjusting range proper locates above this level, and it istaken care of by means of a movable plate part, the overflow edge ofwhich is likewise maintained in horizontal position.

The above described aqueous solution chutes provided with overflow edgesinclude some drawbacks. Two plates moving against each other cannot bemade compact, but a remarkable part of the overflow, about 10-40%thereof, passes along some other route than over the overflow edge.Therefore the adjusting of the phase boundary surface works properlyonly when the solution feeds surpass about half of the amount for whichthe extraction plants are designed. Moreover, when driving down theprocess, the above described overflow causes a solution flow to the nextprocess step and thus weakens the extraction results in connection withthe next drive up. There is also the danger that the boundary surfacesof the separation parts fluctuate, in which case a phase dispersioncarrying impurities and located in between pure phases is transportedalong with the separated solutions.

SUMMARY OF THE INVENTION

By means of the method and apparatus of the present invention, we havenow attempted to avoid the above described drawbacks, and the object isto improve the accuracy in the adjusting of the boundary surface inbetween the solutions, and at the same time prevent an aeration of thesolutions and thus to improve the controllability of the flow of theseparating solutions. A good adjustability is particularly importantwith liquid—liquid extraction, when driving the process up an down.According to the invention, the boundary surface between the solutionsis adjusted by adjusting the overflow surface, so that in the bottompart of the aqueous solution end, there are installed several verticallyadjustable tubular members, whereto the aqueous solution flows from thedownwardly direction and is discharged to the surrounding aqueoussolution chute through the top element of the tubular member. Theaeration of separated solutions is prevented by means of a structurewhere the settled solution flows from the solution end via a shaft-likeweir box positioned lower than the bottom of the solution end to thetubular lines. The prevention of aeration is important particularly forthe extraction solution. Said weir box can also be provided withadditional structures for avoiding the creation of vortexes and theabsorption of air into the solution through them. The essential novelfeatures of the invention are apparent from the appended patent claims.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in more detail with reference to the appendeddrawings, where

FIG. 1 is a schematical illustration of the cross-section of theseparation part, i.e. of the settler, in the longitudinal direction,

FIG. 2 illustrates the structure used for discharging the aqueoussolution,

FIG. 3 is a top-view illustration of the discharge end of the settler,

FIG. 4 shows the structure of the discharge end of the settler incross-section,

FIG. 5a illustrates the structure used for discharging the extractionsolution in cross-section, and

FIG. 5b is a side-view illustration of the same structure,

FIG. 6a is a schematical side-view illustration of a preferredembodiment of the same structure, and

FIG. 6b is a top-view illustration of the same structure,

FIG. 7a illustrates the liquid seal used in the discharge of theextraction solution in cross-section, and

FIG. 7b is a top-view illustration of the object of FIG. 7a.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematical illustration of the structure of the separationpart, i.e. of the settler 1. A dispersion 2 of two different phasesmixed in the mixing unit, i.e. the mixer (not illustrated in thedrawing) flows into the settler which at its front end is provided withpicket fences 3, 4 and 5. When flowing forward, the dispersion isgradually divided into two separate layers, an upper organic phase layer6 and a lower aqueous solution layer 7. In between the phases, thereremains a continuously thinning dispersion layer. Part of the aqueoussolution can be removed into circulation from the settler after the lastpicket fence 5 through the collecting channel 8. The organic phase isremoved from the settler as overflow to the chute 9 of the lighterphase, the front end of said chute being fixed, but advantageouslyrounded according to the drawing. The aqueous solution continuesproceeding from underneath the organic phase chute to the water end 10of the aqueous solution phase. The aqueous solution rises to the waterend first through tubular members 11 and from inside them as overflow tothe water end 10 proper.

The advantageous discharge method of the aqueous solution according tothe invention is described in more detail in FIG. 2. The aqueoussolution flows through a duct 14 formed by the lower bottom 12 of thewater end 10 and the settler bottom 13 to the lower tubular element 15of the tubular member 11, which element 15 is telescopically connectedto an upper tubular element 16. Advantageously the top edge 17 of thetop element is constructed to be upwards expanding, so that the overflowspeed can be reduced by means of this structure and the adjusting madeeven more accurate.

In order to connect the telescopically joined tubes 15 and 16 in acompact fashion, the structure can be further secured by attaching onthe tube surfaces a bellow-like element 18 connecting the tubes to eachother. The height of the bellow-like element is such that it enables therising and lowering of the tubes in relation to each other throughoutthe length of the adjusting range. The lower element 15 of the overflowpipe 11 is compactly attached to the lower bottom 12. The lower bottomitself is advantageously located at the same height as the bottom of theorganic solution discharge chute 9. By employing the method illustratedin the drawing, it is thus possible to adjust the height of the aqueoussolution surface in an accurate and controlled manner withoutuncontrolled solution flows over the adjusting edge, and at the sametime there is adjusted the height of the boundary surface between thesolutions.

FIG. 3 is a top-view illustration of the phase discharge end, in whichcase there is located, first in the flow direction, the organic phasedischarge chute 9 and thereafter the water end 10 of the aqueoussolution. In the drawing it is seen that the overflow height of thetubular members 11 can be adjusted in groups of several pieces by meansof an adjusting bar 19. In the drawing, to the adjusting bar 19 thereare connected three overflow pipes 11, but the number can naturallyvary. In FIG. 4 the same phase discharge end is shown in cross-section.In between the overflow pipes, there are seen supporting structures ofthe discharge end.

In the discharge end of the settler, there is thus formed, according tothe present invention, a uniform aqueous solution space 10, restricted,when seen in the flowing direction of the solutions, at the front end bythe organic phase overflow chute 9, and at the final end by the rear endof the settler 1 and at the sides by the side walls of the settler. Asis apparent for instance from FIG. 3, the overflow pipes 11 are locatedside by side in the water end 10. The number of the overflow pipes isadjusted to be such that the flow speed in the overflow pipes is setwithin the range 0.3-0.7 m/s.

Large copper extraction plants include process steps where the externalfeed of the aqueous solution into the step, and respectively thedischarge of aqueous solution from the step, is remarkably smaller thanthe quantity of extraction solution flowing from one step to the next.Because the solution contact performed in the mixer between the organicand aqueous solution takes place roughly in a ratio 1:1, and still theaqueous solution feed from outside the step into the mixer is slight,the major part of the aqueous solution must be fed in through thesettler part of the same step. In connection with FIG. 1, there wasmentioned the collecting channel 8, through which the major part of theaqueous solution can advantageously be absorbed into circulation, andthus the aqueous solution needed in this recirculation does not chargethe discharge end 10 of the aqueous solution. In that case the water end10 is needed only for circulating the aqueous solution going to externalrecirculation. For instance in the extraction solution washing step theexternal supply of aqueous solution is of the order 50 m³/h, althoughthe aqueous solution supply into the mixer is of the order 1,000-2,000m³/h. In that case it is clear that the number of overflow pipes 11required in the water end 10 is fairly small. It is likewise possible incorresponding cases to reduce the transversal area of the overflow chutewithout making the water end narrower.

The removal of the separated solutions from the extraction solutionchute and from the water end, and the conducting of the solutions to thenext process step, is according to the invention arranged so that thesolutions and particularly the extraction solution 6 are transferred tothe next step by avoiding the aeration of the solution. In FIGS. 3 and 4it is seen how the extraction solution chute 9 continues in the sidewaysdirection in a way to outside the settler proper, and through this outerweir box 20 of said chute the solution is conducted to the next processpoint. According to FIGS. 5a and 5 b, the weir box 20 of the extractionsolution chute is in a shaft-like fashion deeper than the chute 9itself, and an extraction solution transfer pipe 21 is connectedthereto, at the bottom part of the weir box. Instead of one, the numberof transfer pipes can be for instance two, in which case theconstruction of oversized circulation pipes is avoided. The two-pipestructure has the advantage that there are avoided situations where forexample the bottom part of one large pipe of organic solution is filledwith aqueous solution that can plug the proceeding of the extractionsolution. The weir box of the extraction solution chute isadvantageously located at either side of the settler, but thecorresponding shaft-like weir box of the aqueous solution can be placedfreely at the rear wall of the water end, or on either side of the sideend of the water end 10.

As was mentioned above, the removal structure 20 of the aqueous solutioncan be located at different spots in the chute. The location depends onwhich step is in question and where the aqueous solution is conductednext. It is naturally sensible to place the removal point in a locationwhere the number of transfer pipes to the next step is as small aspossible. A shaft-like structure enables a horizontal outlet of thepipework connected to the structure on a level as high as possible, inwhich case pumping becomes easier and deep pipework excavations can beavoided. A remarkable advantage is already the fact that the pipes canbe drawn on ground surface.

The shaft-like weir box 20 prevents air from entering the solution. Inorder to prevent air from entering, the structure can be furtherimproved by providing the ceiling part of the weir box with downwardlyoriented and essentially vertical plates 22 in front of each pipe outlet21. It is in fact advantageous to install the plates so low that theextraction solution chute is nearly full, in which case the chute doesnot absorb air. Another additional preventive method for the absorptionof air is a lattice channel 24 located in the vicinity of the liquidsurface and illustrated in FIGS. 6. This obstacle is useful when drivingwith an incompletely filled extraction solution chute or water end andworks in a circulation-attenuating fashion also in normal runs, which donot officially need said obstacles. The lattice channel 24 is arrangedso that its top end extends to above the liquid surface, but it can alsobe located underneath the liquid surface, even as much as for the lengthof the lattice channel.

The use of the removal structure 20 prevents air from being absorbedinto the solutions to be discharged. The structure is shaft-like, andthe bottom 23 of the structure is located lower than the bottom of thesolution chute, so that the height difference is 0.3-1.0 times the chutewidth.

In large extraction plants, the extraction solution storage tank isgenerally located in a separate storage tank area, which is placed solow that the solutions are made to flow there by applying free release.This is often carried out with a drop of several meters, and leads to anintensive aeration of the solution. From FIGS. 7a and 7 b it is seen howaeration can be prevented, particularly in pipeworks to be conductedinto storage tanks by using a liquid seal, which is installed in theextraction chute 9, prior to the removal structure 20. The question isof an elongate overflow 25, which in a way forms a chute in thedischarge chute, in the middle of the outlet end. Loosely around theoverflow there is constructed a vertical plate 26 extending remarkablylower than the liquid surface. Advantageously these arise as far as theedge of the extraction solution chute, and from there starts a cover 27,illustrated in FIG. 7b, which continues towards the solution dischargedirection and extends in a uniform shape over the discharge shaft 20,too. The pressure of the air space left underneath the cover isequalized by means of a vertical pipe 28 leading to this space.

The above described overflow to be conducted to the storage tank can behorizontal or evenly descending towards the incoming direction, whilethe lowest part is formed of the section crossing the extractionsolution chute, and the topmost part of the overflow sections borderingthe discharge shaft. From the point of view of flow technology, thelatter solution is more recommendable, because it reduces the dropheight of the overflow and thus limits the mixing of air into theextraction solution. However, the danger of mixing is clearly smallerwhen using a liquid seal described above.

In the above specification we have described the method and apparatusaccording to the invention mainly with reference to copper extraction,where large extraction plants are used, and attempted to find solutionsto their problems. It is, however, clear that the method and apparatuscan be applied to other extraction plants, too.

What is claimed is:
 1. A method for adjusting the boundary surfacebetween two mutually gravity separable solutions and conducting theseparated solutions out of a discharge end of a settler where gravityseparation takes place, which comprises introducing said solutions intoa settler, allowing the solutions to separate by gravity, maintainingthe height of a separated lighter solution constant, adjusting theheight of a separated heavier solution by conducting said separatedheavier solution upwardly through height adjustable tubular members,removing the separated solutions from the part of the settler whereseparation takes place so as to prevent aeration of said solutions byconducting said solutions to transfer pipes through covered weir boxesthat are deeper than the discharge end of said settler.
 2. A methodaccording to claim 1, wherein the aeration of said solutions isprevented by turbulence-preventing plate structures arranged in the saidweir boxes.
 3. A method according to claim 1, wherein the aeration ofsaid solutions is prevented by turbulence-preventing lattice structuresarranged in the said weir boxes.
 4. A method according to claim 3,wherein the lattice structure is installed so that its top edge islocated above a liquid surface.
 5. A method according to claim 3,wherein the lattice structure is installed so that its top edge islocated beneath a liquid surface.
 6. An apparatus for preventingaeration of two gravity separable liquid solutions obtained from aliquid—liquid extraction comprising a settler for separating saidsolutions of different densities, a lighter solution discharge chute, aweir box connected to said chute, said weir box having a top part and abottom part, said weir box being deeper than said chute and the bottompart of said weir box being connected to a transfer pipe of the lightersolution, a heavier solution discharge end, a weir box connected to saiddischarge end and the bottom part of said weir box being connected to atransfer pipe of the heavier solution.
 7. An apparatus according toclaim 6, wherein said weir box connected to the extraction solutionchute is in the sideways direction installed as a continuation of theextraction solution chute.
 8. An apparatus according to claim 6, whereinsaid weir box connected to said heavier solution end is in the sidewaysdirection installed as a continuation of said end or at the rear wall ofsaid end.
 9. An apparatus according to claim 6, wherein the number ofthe transfer pipes starting from said weir box is two.
 10. An apparatusaccording to claim 6, wherein the ceiling part of said weir box, havedownwardly protruding, vertical plates corresponding to the number ofthe transfer pipes.
 11. An apparatus according to claim 6, wherein saidweir box is provided with a lattice channel arranged in the vicinity ofa liquid surface.
 12. An apparatus for preventing aeration of twogravity separable liquid solutions obtained from a liquid—liquidextraction comprising a settler for separating said solutions ofdifferent densities, a lighter solution discharge chute, a weir boxconnected to said chute, said weir box having sidewalls, said weir boxbeing deeper than said chute and a transfer pipe of said weir box beingconnected to a lower part of a sidewall of said weir box, a heaviersolution discharge end, a weir box connected to said discharge end and atransfer pipe of the heavier solution connected to a lower part of asidewall of said weir box.